Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.
Hello card()
A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).
At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.1 For example, the code to the right generates HTML that is identical to the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Lorem porta a sociosqu elementum. Integer class sagittis fermentum porttitor orci. Ante aliquam aptent primis sem – nisl faucibus, nam praesent. Lacinia sem natoque aptent curabitur eros dis eros nisl orci euismod. Vulputate inceptos curabitur senectus in, vitae praesent tellus netus sed dapibus fermentum, litora vestibulum erat potenti nulla.
Dolor turpis blandit torquent fringilla arcu montes. Turpis pharetra suscipit nisi sociis sociosqu, luctus litora enim aptent eros. Egestas sem venenatis vulputate rhoncus eros, luctus maecenas vel. Duis suspendisse torquent vel vestibulum dictum. Pellentesque neque purus dui cubilia magnis, potenti volutpat cubilia at bibendum sed.
Amet id condimentum eros, aliquet dignissim senectus augue molestie. Iaculis venenatis urna platea, risus phasellus egestas? Enim platea morbi volutpat; pharetra interdum, primis justo lacinia interdum felis mus. Penatibus habitasse pharetra nec dictumst, rutrum morbi aliquet phasellus. Integer molestie cubilia interdum fames litora eu urna nunc aliquam!
Filling outputs
A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.
This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s, which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Consectetur erat eu blandit ac ante aenean? Dictum dictumst velit mus mauris tellus nostra taciti viverra? Quisque nec non odio conubia, etiam dapibus convallis etiam? Feugiat cursus at purus lacinia cubilia suscipit, varius dui enim luctus varius! Natoque faucibus ad eros tincidunt justo eget et sociosqu, montes non, diam lectus, senectus quam, justo euismod quisque.
Adipiscing pharetra tellus venenatis enim quis tempor mollis non fusce bibendum faucibus! Mauris ante neque aptent quisque: vulputate erat commodo fames ut, suspendisse taciti odio. Id nullam faucibus dictumst; porttitor laoreet ullamcorper torquent. Pharetra habitant torquent nibh feugiat taciti risus parturient. Ante enim torquent, senectus molestie nisi urna metus nostra non, quis aptent lacinia eget conubia.
Elit dui gravida augue – semper erat consequat mollis, molestie vel vitae blandit! Ornare euismod mauris massa vel tellus ad commodo libero? Orci cras velit tortor habitant vulputate parturient neque cubilia varius accumsan mattis! Phasellus bibendum condimentum curabitur fermentum pellentesque nascetur arcu et, maecenas netus semper. Elementum integer vel – dui nec, venenatis potenti vitae odio enim morbi conubia.
Consectetur ante fermentum euismod porta dis faucibus etiam condimentum. Vestibulum id pulvinar condimentum vestibulum inceptos porttitor proin? In vestibulum ut, maecenas rhoncus malesuada lacus sagittis blandit inceptos. Luctus dapibus neque nostra nisi euismod sem nec nibh enim. Laoreet purus lacinia libero ornare cum rutrum tortor ad rutrum ligula!
Amet facilisis faucibus euismod euismod accumsan ornare proin auctor eget magna? Eget ultrices lobortis mi, pharetra metus odio cursus, a etiam sagittis? Condimentum ullamcorper suspendisse eu sodales tristique felis pharetra, tempus fusce ridiculus libero nisl. Eros cum quis urna morbi fusce erat odio posuere fermentum platea luctus donec. Interdum conubia eros sociis justo accumsan tincidunt conubia ac.
Lorem tincidunt orci feugiat posuere integer vitae laoreet eget felis scelerisque, ridiculus eleifend placerat. Ultricies accumsan nisi semper bibendum pulvinar dapibus quam porttitor malesuada suscipit ultricies. Justo fermentum, montes ligula consequat gravida sollicitudin sapien; fermentum nulla dis. Etiam augue nascetur, sem potenti maecenas sociosqu orci augue diam ridiculus parturient? Porttitor vulputate phasellus viverra taciti ridiculus ultrices ut.
Lorem quam nunc blandit, lacinia orci nunc interdum inceptos. Dictum tincidunt parturient magna senectus varius iaculis. Ultrices felis quam quisque est nulla – himenaeos purus. Turpis pretium elementum molestie suscipit quis nibh tempor class fermentum. Dis at cum, platea sem nostra dui iaculis euismod integer cubilia faucibus nisi fusce nisi in curae.
Dolor nisl: dapibus imperdiet nisl feugiat suspendisse ridiculus in. Erat praesent faucibus mi imperdiet blandit. Hendrerit ultricies accumsan montes nunc urna tincidunt nec diam fermentum fames? Arcu vitae luctus rhoncus, aptent laoreet netus viverra ridiculus: vivamus lectus cursus, blandit pretium magnis ligula! Cursus cursus ullamcorper vivamus vehicula.
Adipiscing tempus eu erat eu, integer sociis hendrerit torquent per vivamus ad. Vestibulum eget natoque nunc, accumsan turpis sed. Ac orci dignissim praesent diam – conubia, magnis faucibus sodales consequat! Dui vulputate facilisis pulvinar platea dignissim tristique curabitur, pulvinar pulvinar nec faucibus sociis. Non conubia?
Amet pellentesque, dignissim per tempor facilisi aliquam ad, scelerisque justo dictum. Varius ullamcorper neque urna quisque ultricies dapibus, sodales orci? Vivamus nisi laoreet pharetra at vulputate sodales lectus ultrices? Tortor in risus lectus dui est, pretium, mi curae senectus. Vehicula odio, vivamus nisi sodales felis vestibulum lacinia id, egestas eget convallis non quam aliquet.
Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Sit porttitor augue etiam taciti commodo, fermentum inceptos consequat neque velit; placerat consequat. Vehicula dictum curae consequat ac ultrices condimentum dictum consequat? Integer himenaeos eu porta nullam curabitur, odio tristique facilisi aliquam nisi mauris taciti sed inceptos. Faucibus tellus platea pharetra urna vivamus at turpis! Ornare morbi mauris in id dapibus mi.
Consectetur sem eu platea integer tempus rutrum lectus placerat. Netus eros dignissim turpis faucibus aliquet turpis pretium dictum morbi. Netus duis luctus nec risus nibh nisl accumsan volutpat. Mollis platea condimentum aliquam ac ultricies gravida rutrum. Parturient nunc phasellus rhoncus ante pretium, vestibulum phasellus sociis – senectus magna.
Lorem egestas consequat conubia condimentum, vulputate volutpat quis nam, tempor aenean hac natoque. Congue metus torquent, praesent sem nisi erat nibh vestibulum montes. Gravida ornare ligula integer eleifend taciti dictum etiam porttitor! Fermentum dignissim enim, nunc feugiat quis pharetra risus, libero facilisis at! Lacinia consequat facilisi tristique vulputate aliquam – feugiat lacinia natoque; duis primis taciti!
Multiple cards
layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navset_card_tab() and navset_card_pill() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav_panel() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().
library(leaflet)
navset_card_tab(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav_panel(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav_panel(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav_panel(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar = sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)Flexbox
Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)Here's a simple hyperlink.
In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.